MODULDE 5: TWO LED FLASHER

 EMBEDDED C   TUTORIAL

                                TIMOTHY ADEGBITE

Welcome to today’s Trinnex electronics tutorial on Embedded C. Apologies for the long break. I have been busy with some studies, researches and personal development that has literally taken most of my time. Thanks to all, that has been following up with my blog, thanks for all the chats and comments. It shows there are people who are really passionate about what I am doing. You can always post your comments here or talk to me privately on anything involving electronics and embedded Programming.

Remember, this is a place for startups in electronics and embedded system programmers. If you think you are not a startup and you need more advance tutorial or support on your projects, you can send me a mail or chat with me, I will gladly reply you.

Today, I will continue on the LED BLINK TUTORIAL. I will be flashing two led at a specified interval using a delay function. This can be accurately achieved with the use of a timer interrupt, a built-in function of the microcontroller. Using the interrupt is a subject for another day. The delay function is also accurate, but the interrupt function is more accurate and precise.

We will be improving on the program written before, which was flashing an LED. We will be including one more LED.

This time, we will be flashing two LED alternatively at the interval of 2 secs. To achieve this, we make the delay function last for a total of 2 secs. The delay function can either be in milliseconds (ms) or microseconds (us). To implement the delay in milliseconds, you use  “ __delay_ms( ) ” , to implement the delay in microseconds, you use “ __delay_us( ) ” . The value in the bracket signifies the duration of the delay.

For example, if I want a delay of 200ms, I simply type  __delay_ms(200). To implement a delay of 2us, I simply type __delay_us(2).

To implement a delay of 2secs, what do I do? I simply do a conversion from seconds to milliseconds. You know that 1000milliseconds makes 1seconds. So meaning, 2000milliseconds makes 2 seconds.

So, to implement a delay in seconds, you simply do a conversion from seconds to milliseconds, then put the value into the bracket. A delay of 2seconds is equal to 2000milliseconds, to implement this, you simply type  __delay_ms(2000).

Below shows the simply program written to achieve this.

//This is a simple project, demonstrating the blinking of an LED 
//using the pic16f84a microcontroller.

#include     <  xc.h   >                      // header file that includes all the
                                                       //files in the pic16f84a

#define _XTAL_FREQ 4000000    // clocking frequency is 4Mhz

void main(void)                    //  This is the main function. It receives 

                                           // no argument and  returns no value. 
                                           //  It is a void function.

{

    TRISA=0B00000000;      // equates all PORTA as an output port

    TRISB=0B00000000;     // equates all PORTB as an output port

    PORTA=0;                     // clears PORTA bits

    PORTB=0;                     // clears PORTB bit

    while(1)                        // while loop;  it iterates continuously

    {

        PORTBbits.RB0 = 1  ;      // set bit 0 of PORTB

        PORTBbits.RB1 = 0 ;     // clears bit 1 of PORTB

        __delay_ms(2000);       // delay for 2000ms

        PORTBbits.RB0 = 0 ;     // clears bit 0 of PORTB

        PORTBbits.RB1 = 1 ;     // set bit 1 of PORTB   

        __delay_ms(2000);       // delay for 2000 ms   

    }

}

After compiling this program and running it on Proteus, you will find the two LED blinking alternatively.  One of the important thing you should learn here is how to implement a delay function and how to assign values to the ports of the microcontroller, which I have explained in the former tutorials.

In the next tutorial, I will be working on a LED chaser, but before then, I have a little task.

ASSIGNMENT:

Try flashing 3 LEDs alternatively at the interval of 1 sec, post your codes here, to see how efficient your code is and I will give my comment on how it can be improved on. Remember, there is not short cut to knowing this than constant practice!!!

The next tutorial and the solution to the assignment will be available a week from now.

Below shows the finished prototype of the design on Proteus.

You can always post your comments here, for further clarifications and questions.